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Study of the initial stages of gelation phenomena by Diffusing wave spectroscopy (DWS) (CAT#: STEM-MB-0837-WXH)

Introduction

In polymer chemistry, gelation (gel transition) is the formation of a gel from a system with polymers. Branched polymers can form links between the chains, which lead to progressively larger polymers. As the linking continues, larger branched polymers are obtained and at a certain extent of the reaction links between the polymer result in the formation of a single macroscopic molecule. At that point in the reaction, which is defined as gel point, the system loses fluidity and viscosity becomes very large. The onset of gelation, or gel point, is accompanied by a sudden increase in viscosity. This "infinite" sized polymer is called the gel or network, which does not dissolve in the solvent, but can swell in it.




Principle

Diffusing-wave spectroscopy (DWS) is an optical technique derived from dynamic light scattering (DLS) that studies the dynamics of scattered light in the limit of strong multiple scattering. DWS is able to give information about the local dynamics of particle dispersion in a highly turbid medium. It has been widely used in the past to study colloidal suspensions, emulsions, foams, gels, biological media, and other forms of soft matter. If carefully calibrated, DWS allows the quantitative measurement of microscopic motion in a soft material, from which the rheological properties of the complex medium can be extracted via the microrheology approach.
The technique of DWS depends on the scattering of light from highly turbid suspensions. A sample of the suspension is illuminated by light from a laser and the incoming photons are multiply scattered. This scattered light is detected and subjected to autocorrelation analysis.

Applications

• Diffusing Wave Spectroscopy (DWS) is an advanced light scattering technique, which is primarily applied for microrheology and particle sizing.
• DWS has been applied in biomedical and clinical areas, especially in monitoring cerebral blood flow (CBF).

Procedure

1. Sample Preparation
2. Diffusing Wave Spectroscopy Testing
3. Data analysis

Materials

• Diffusing wave spectroscopy (DWS) instrument
• DWS RheoLab